The present invention relates to a vehicular lamp unit, and a manufacturing method therefor, in which a front lens and a lamp body are directly bonded together.
Conventionally, two types of methods for bonding a front lens and a lamp body of a vehicular lamp unit have been well known, that is, indirect bonding via a seal member (for example, the hot melt sealing method), and direct bonding by bringing the two members into direct abutment (for example, heating plate welding, vibration welding, ultrasonic bonding, or the like).
As a direct bonding method, laser beam welding has been well known in other technical fields. This method is applicable to the bonding of a front lens and a lamp body using the process as described below (see also commonly assigned U.S. patent application Ser. No. 09/548,361).
Referring to FIG. 7, a seal leg 2a extending in the outward direction along the outer periphery of a front lens 2 is formed. A receiving surface 4a is formed along the opening portion of the front end of a lamp body 4. The lamp body 4 is placed on a receiving jig 102. The front lens 2 is set onto the lamp body 4 in such a manner that an end surface 2b of the seal leg 2a is brought into abutment against the receiving surface 4a. The front lens 2 is further covered with a transparent pressure plate 104 through which the front lens 2 is pressed to the lamp body 4. In the above state, a laser beam L is irradiated onto the receiving surface 4a from a position upward of the front lens 2 through the transparent pressure plate 104 and the seal leg 2a. As a result, the receiving surface 4a is heated and melted by the irradiation energy of the laser beam L so as to fuse with the end surface 2b of the seal leg 2a that has been melted by the heat. The front lens 2 and the lamp body 4 thus are bonded together by scanning the laser beam L along the seal leg 2a over the entire length of the front lens 2.
Employing the above-described laser beam welding method allows bonding of the front lens 2 and the lamp body 4 without generating burrs on the respective bonded surfaces, resulting in an improved quality of the outer appearance of the area around the peripheral portion of the bonded surfaces. However, the use of this welding method may result in the following disadvantages.
That is, for reliably bonding the front lens 2 and the lamp body 4 together through laser beam welding it is essential to bring the edge surface 2b of the seal leg 2a into abutment against the receiving surface 4a of the lamp body 4 over the entire length of the bonded surface by pressing the front lens 2 towards the lamp body. If, however, the edge surface 2b of the seal leg 2a or the receiving surface 4a has a wave-like irregularity owing to insufficient smoothness, gaps are created in the areas therebetween, even while pressure is being applied, resulting in bonding failure.
The bonding width of the bonded surface between the front lens 2 and the lamp body 4 is determined by the beam spot diameter of the laser beam L irradiated onto the receiving surface 4a of the lamp body 4. It is desirable that the beam spot diameter be set to a relatively large value such that the bonding strength can be enhanced. Since the laser beam L is irradiated onto the receiving surface 4a through the seal leg 2a, the dimension of the beam spot diameter is limited by the width of the seal leg 2a. 
The invention has been made in view of the foregoing circumstances. It is therefore an object of the invention to provide a vehicular lamp unit, and a manufacturing method therefor, in which the front lens and the lamp body are directly bonded together so as to improve the quality of the appearance of the area around the peripheral portion of the bonded surface, prevent bonding failure between the front lens and the lamp body, and enhance the bonding strength therebetween.
The aforementioned object is realized by the invention by employing laser beam welding as the method for bonding the front lens and the lamp body together and by suitably establishing the configuration of the peripheral portion of the bonded surfaces.
A vehicular lamp unit of the invention having a front lens and a lamp body directly bonded together is characterized in that a seal leg is formed on the outer periphery of the front lens and a receiving surface that is brought into abutment against an end surface of the seal leg is formed on the lamp body, the end surface of the seal leg and the receiving surface are directly bonded together through laser beam welding, and the bonded surface is inclined at a predetermined angle with respect to a plane perpendicular to the reference angle of the lamp unit.
The term xe2x80x9claser beam weldingxe2x80x9d indicates a bonding method wherein a laser beam transmitting member that allows permeation of the laser beam is brought into abutment against a laser beam non-transmitting member that does not allow permeation of the laser beam, both members are pressed together generally in the direction of the reference axis, and a laser beam is irradiated onto the abutment surfaces of the two members through the laser beam transmission member so as to heat the laser beam non-transmission member. As a result, both members are fused together. The laser beam used for the laser beam welding is not particularly limited, and, for example, a semiconductor laser, a YAG laser or the like may be employed.
The material for forming the lamp body is not particularly limited so long as it does not allow transmission of the laser beam and is heated and melted by the laser beam irradiation. For efficient laser beam welding, it is preferable that the lamp body is formed of a black-colored material to which an auxiliary material such as carbon black has been added so as to enhance the laser beam absorbing capability of the lamp body.
Also, the material for the front lens is not particularly limited so long as it allows transmission of visible light and the laser beam and it can be fused and fixed to a lamp body that has been melted.
The numeric value of the angle of inclination of the bonded surface is not limited so long as such surface is inclined with respect to a plane perpendicular to the reference axis of the lamp unit. The direction of inclination of the bonded surface may be either inward or outward of the front lens. The bonded surface further be formed in a V- or W-like shape.
The vehicular lamp unit according to the present invention has a structure in which the front lens and the lamp body are directly bonded together. The direct bonding is accomplished through a laser beam welding process, and the bonded surfaces are the edge surface of the seal leg formed along the outer periphery of the front lens and the receiving surface formed on the lamp body. This allows bonding without generating burrs on the respective bonded surfaces, thus improving the quality of the outer appearance around the bonded surface.
In addition, the vehicular lamp unit according to the present invention provides the following operational effects owing to inclination of the bonded surface at a predetermined angle with respect to a plane perpendicular to the reference axis.
That is, in the case where gaps are created between the edge surface of the seal leg of the seal leg or the receiving surface having wave-like irregularity owing to insufficient smoothness, the pressure acting on the members to be bonded causes slippage between the members because the bonded surface is inclined. The slippage serves to seal the gaps created in the areas between both members so as to enable abutment thereof over the entire length of the bonded surface. Accordingly, bonding failure is prevented.
The bonding width of the bonded surfaces between the front lens and the lamp body is determined by the beam spot diameter of the laser beam irradiated onto the receiving surface of the lamp body. Since the bonded surfaces are inclined at a predetermined angle with respect to a plane perpendicular to the reference axis of the lamp unit, the beam spot diameter is increased by an amount corresponding to the angle of inclination. As a result, the bonding width of the bonded surface is increased, contributing to an enhancement of the bonding strength by an amount corresponding to the increased width.
The vehicular lamp unit according to the invention having the front lens and the lamp body directly bonded together prevents bonding failure therebetween and enhances the bonding strength while improving the quality of the outer appearance of the portion around the bonded surfaces.
Assuming that, in the aforementioned structure, the receiving surface of the lamp body is further provided with ribs that protrude generally in the direction of the reference axis of the lamp along a side surface on an edge acute-angled portion side of the seal leg of the front lens, the abutment between the ribs and the seal leg prevents the generation of unnecessarily excessive slippage between the edge surface and the receiving surface caused by the pressure applied between the front lens and the lamp body. In addition, part of the laser beam irradiated onto the receiving surface of the lamp body is reflected internally off the edge surface of the seal leg. This internally reflected light is directed to strike a side surface of the ribs so as to heat and melt the ribs, which allows the side surface of the ribs and the side surface on the edge acute-angled portion side of the seal leg to constitute a second bonded surface. This further enhances the bonding strength between the front lens and the lamp body.
Assuming that, in the aforementioned structure, that the angle of inclination with respect to the plane perpendicular to the reference axis of the lamp unit of the bonded surface is in the range from 40 to 50xc2x0, the applied pressure is effective not only to easily generate slippage between the edge surface of the seal leg and the receiving surface but also to enlarge the bonding width of the bonded surfaces. Moreover, the ribs formed on the lamp body allow the laser beam that has reflected internally off the edge surface of the seal leg to strike the side surface of the ribs efficiently in a substantially vertical direction. This enhances the bonding strength between the side surface of the ribs and the side surface on the side of the edge acute-angled portion of the seal leg.